People in southern Somalia are starting to die from thirst in the worst drought in over 40 years in some parts of the country, says aid agency Oxfam.
People are walking up to 70km in search of water
Oxfam says assessment teams found seven people who died of dehydration, and that tens of thousands are now at risk.
People are surviving on the equivalent of three glasses of water a day, in temperatures of over 40C (100F).
Oxfam reports an almost unprecedented situation, where people beg for water along the sides of the road.
All surface water has gone, boreholes are running dry, and people are walking up to 70km (45 miles) in search of water.
The 830 ml available per person per day has to be used for drinking, cooking and washing.
"The situation is as bad as I can remember. Some people are dying and children are drinking their own urine because there is simply no water available for them to drink," Somali village elder Abdullahi Maalim Hussein told Oxfam.
Schools and local groups have collected $100,000 - a large sum in an impoverished country - to pay for a relief effort.
Livestock in the south have been dying because of hunger
On Wednesday 10 water tankers left the capital, Mogadishu, with supplies for the worst hit regions in the south.
Oxfam says it will launch a similar operation next week but is predicting that without water supplies more children will die.
"The situation will get worse unless swift action is taken," said Mohamed Elmi, Oxfam Regional Programme Manager.
"People cannot survive on just three glasses of water a day when the temperature is hitting 40 degrees."
Relief efforts in Somalia are made difficult by a lack of proper roads and the absence of a functioning central government, with control of the country divided among rival militia groups.
The World Meterological Association has warned the Horn of Africa will remain in the grip of a drought until at least April.
The United Nations estimates more than 11m people in parts of Kenya, Ethiopia, Somalia, Eritrea, Tanzania and Burundi need food aid for the next six months.